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Posted for "Christopher Zavatson" <Christopher.Zavatson@udlp.com>:
Gary,
You bring up very good points. I just recently completed new cowl and
cooling approach on my 360 which addressed some of your points. The
results are fantastic: Peak cylinder temps are down 30 degF and speed
is up ~3kts.
1. Pressure recovery. I would guess that more attention is not paid
here due to the increased complexity. My new inlet area is actually
smaller than on the original cowl, but two diffusers, one part of the
cowl and the other part of the engine take the air through controlled
expansion. The cowl split line can no longer run through the inlets
however.
2. The diffusers lead to a fully enclosed plenum chambers which
eliminates the common leak paths. It is difficult to say what
percentage of the improvement should be attributed to reduced leakage
and how much to pressure recovery at the inlet.
3. The pressure drops across individual cylinders are balanced with
aluminum baffle material. If, within the plenum above the engine, the
pressure is high enough, the velocity low enough and pressure drops
equal for all cylinders, the air will indeed "magically get to where it
needs to go". It is very difficult to quantify all of these parameters
so some experimentation is needed. Note: The Lycoming cylinder fins
don't have the blocked fins on one side of the head as is seen on the
Continentals. This, of course, not only adds restriction, but asymmetry
for the cylinder located at the end requiring extra treatment specific
to Continental installations (See Rob Logan's photos).
4 and 5 get more engine and airframe specific. The 320/360s have sharp
edges all along the bottom edge of the firewall, so the ES is already
one step ahead. I have not yet made any changes here - I left that as a
future project.
Chris Zavatson
N91CZ
360 std
Christopher Zavatson
Mobility Technologies
United Defense
(408)289-4329
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